This invention relates to low-emission burners, and particularly to air and fuel mixing nozzles for use in a burner assembly. More particularly, this invention relates to nozzles for discharging a combustible air and fuel mixture into the combustion chamber of a cyclonic combustor.
A cyclonic combustor is a burner which burns a swirling air and fuel mixture that travels at a predetermined velocity along a spiral or helical path inside a combustion chamber. Typically, the combustion chamber is an open cylinder and the air and fuel mixture is introduced through an inlet provided at one end for spiral travel toward an outlet provided at the other end. The swirling air and fuel mixture in the combustion chamber is ignited to produce a flame. In a cyclonic combustor, the fresh unburned air and fuel mixture introduced through the inlet into the combustion chamber continuously mixes with any undischarged products of combustion (e.g., oxides of nitrogen, carbon monoxide, etc.) remaining in the combustion chamber to produce a swirling combustible mixture of combustion air and fuel and products of combustion in the cyclonic combustion chamber.
A cyclonic combustor nozzle for producing a combustible fuel-lean air and fuel mixture which is ignitable in a cyclonic combustion chamber to yield low flame temperatures and low emissions of oxides of nitrogen would be a welcomed improvement over conventional nozzles of the type used in cyclonic combustor. Excess air is present in a fuel-lean air and fuel mixture to provide more material to absorb the heat of combustion so the flame temperature cannot go as high as with a perfect or stoichiometric air and fuel mixture. The oxides of nitrogen produced during combustion contribute to air pollution. Advantageously, low flame temperatures lead to low emissions of oxides of nitrogen.
According to the present invention, a cyclonic combustor nozzle is provided for mixing air and fuel to produce a combustible lean air and fuel mixture. The cyclonic combustor nozzle includes a nozzle body formed to include a fuel chamber and a combustion air chamber and means for conducting combustion air from the combustion air chamber through the nozzle body into a cyclonic combustion chamber of a cyclonic combustor at a predetermined velocity.
A fuel jet system is provided in the nozzle body to deliver fuel from the fuel chamber into the conducting means to mix with combustion air passing from the air chamber into the cyclonic combustion chamber. This fuel jet system produces a fuel-lean air and fuel mixture in the conducting means that is discharged from the nozzle body into the cyclonic combustion chamber. This fuel-lean mixture can be ignited to produce a flame having a low flame temperature which leads to low emissions of oxides of nitrogen and other contaminants.
In preferred embodiments, the nozzle body is formed to include a centrally located round air chamber and a ring-shaped fuel chamber surrounding the air chamber. The nozzle body is configured to connect to an air supply line and a fuel supply line so that combustion air can be supplied to the round air chamber and fuel can be supplied to the ring-shaped fuel chamber.
The nozzle body is also formed to include a plurality of separate discharge passageways for conducting combustion air from the air chamber into the cyclonic combustion chamber and receiving fuel delivered by the fuel jet system. Each discharge passageway extends outwardly from the round air chamber at an angle so that all of the discharge passageways are arranged in a somewhat pinwheel-shaped pattern about the round air chamber. This arrangement of the discharge passageways helps to establish the desirable swirling cyclonic flow pattern of the air and fuel mixture emitted from the discharge passageways into the cyclonic combustor.
The nozzle body is also formed to include many fuel jets that are located so that one or more fuel jets emit a stream of fuel from the fuel chamber into each of the discharge passageways. This fuel mixes with air traveling through the discharge passageway to produce a desirable fuel-lean air and fuel mixture. In preferred embodiments, the air and fuel mixture has an air-to-fuel ratio greater than 15 to 1. Advantageously, the fuel-lean air and fuel mixture produced by a cyclonic combustor nozzle in accordance with the present invention is ignitable in a cyclonic combustion chamber to yield a low flame temperature and lower the emission of unwanted oxides of nitrogen and other contaminants from the outlet of the cyclonic combustion chamber. It will be understood that a nozzle in accordance with the present invention is well suited for use in providing a combustible air and fuel mixture to any type of burner housing.
Also, the fuel jets formed in the nozzle body are configured and arranged to produce a uniformly distributed fuel-lean air and fuel mixture in each discharge passageway. Advantageously, this enhanced mixing in the nozzle body acts to minimize any zones of (1) perfect or stoichiometric air and fuel mixtures or (2) fuel-rich air and fuel mixtures in the discharge passageway and thereby minimize the later formation of zones or pockets of such mixtures in the cyclonic combustion chamber, thereby reducing the likelihood that "hot spots" will develop in the cyclonic combustion chamber.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.